In modern civil commercial aircrafts, the aircraft cabin is divided into several areas which ought/must be ventilated and temperature-controlled independently of one another. Thus, the temperature control can be made dependent on the number of passengers in different areas of the aircraft cabin, for example. This requirement gave rise to the necessity of mixing the fresh air for each of these areas, which are to be temperature-controlled differently, before being fed into the aircraft cabin with a heating air flow whose quantity is regulated according to the temperature level which is to be reached in the respective cabin area.
Previous air mixers, i.e. devices for mixing fresh air and heating air, entailed the problem of the mixing process causing an appreciable increase in the pressure loss in the air supply pipes of the aircraft cabin. As the pressure in these pipes is subject to pressure regulation, the process of mixing fresh air and heating air acts as a disturbance variable on this pressure regulation, which must be minimised. Moreover, heating air is normally fed from a pipe of titanium alloy into a fresh air pipe of glass-fibre reinforced plastics material (GFRP composite), in which the mixing process then takes place. As the temperature of the heating air lies in a range from approximately 200° C. to 260° C. before being fed into the fresh air pipe, a fresh air pipe produced as a GFRP composite cannot withstand the high temperature of the unmixed hot air flow. It is therefore necessary to ensure efficient mixing of the two air flows and a temperature drop associated therewith. Furthermore, the heating air mass flow which is fed into the air supply line of the cabin is regulated with the aid of a temperature sensor which is installed downstream of the mixing zone. A homogeneous temperature profile must therefore be ensured in the air supply line located downstream of the mixing zone in order that the sensor can measure a representative temperature of the mixed air flow.
The mixing process usually takes place either without an auxiliary body (FIG. 1) or with a simply formed auxiliary body (FIG. 2). In case of the air mixer 10 which is illustrated in FIG. 1, fresh air 2 enters the pipe 11 through an inlet opening 12 and is mixed here with heating air 4 which is supplied through a supply opening 14. The mixed air 6 emerges from the outlet 16 of the air mixer 10 and is fed into the aircraft cabin downstream. In this case, a temperature sensor 18 which measures the temperature of the mixed air 6, is located downstream of the mixing zone. A disadvantage of the air mixer 10 of FIG. 1 lies in the insufficient mixing of fresh air 2 and heating air 4, in particular when the heating air flows are small. The insufficient mixing results in the formation of so-called “hot spots”, which are of disadvantage for the pipe 11 made of a GFRP composite.
An air mixer 20 with an auxiliary body 24 is shown in FIG. 2. A perforated pipe end piece 24 is inserted laterally in the pipe 21 in this air mixer 20. The perforated pipe end piece 24 comprises a plurality of heating air supply openings 25 through which the heating air 4 passes into the pipe 21 and is mixed here with the fresh air 2 entering through the inlet 22. The mixed air 6 emerges from the pipe 21 through the outlet 26. The temperature of the mixed air 6 is again measured by means of a temperature sensor 28. A disadvantage of this air mixing lies in the fact that high pressure losses occasionally occur in the mixing zone, these being caused on the one hand by the reduction of the flow cross section of the pipe 21 in the area of the perforated pipe end piece 24, and on the other by the additional mass flow of heating air 4 entering in this area. As the flow speed in the area of the reduced flow cross section is higher than in other areas with a larger flow cross section, the pressure drops in an area of this kind. Moreover, the additional heating air mass flow 4 brings about a pressure drop in the pipe 21 in the area of the perforated pipe end piece 24. This pressure drop is of disadvantage for the pressure regulation in the fresh air supply lines of the aircraft cabin.
It is therefore an object of the present invention to propose a device with which the process of mixing fresh air and heating air can be carried out with low pressure losses and with a high mixing quality, in particular when large heating air mass flows are to be admixed with the fresh air flow.